The development of speech is being studied in normal children from 3 weeks to 5 years by means of quantitative acoustic measurements. Our data indicate the presence of both innate mechanisms and an interactive adult-child component that aids in the acquisition of a phonologic feature contrast. Quantitative data reveal continuity between babbling and the phonologic stage. The formant frequencies of childrens' vowels are scaled to their shorter supralaryngeal vocal tracts and fall as they mature, but the formant frequency patterns and vowel durations gradually become "well formed". The process continues through late stages of phonologic and syntactic development. The formant frequencies that occur in childrens' words are much higher than those of adult speech and are similar to those that specify vowels in late babbling. The data are consistent with the presence of an innate perceptual mechanism that takes into account vocal tract length. Computer implemented VOT (voice onset time) measurements of the speech of children and the speech directed at them by their mothers indicate that children initially derive this phonological contrast systematically, despite the fact that input from adults is variable and inconsistent; the process again appears to be based on innate perceptual mechanisms. However, mothers provide "hypercorrect" forms when their children enter the phonologic, word using, stage of development. We will derive fundamental, formant, burst frequencies and durational data that will further test and develop theories that account for both the development of speech production and the internal structure of human phonetic and phonologic ability. These normative acoustic data are also essential precursors for the development of procedures for the early diagnosis and treatment of anomalies.